The present invention relates in general to photoelectric controlling and more particularly concerns novel apparatus and techniques for photoelectrically controlling relatively high power levels with compact reliable solid-state apparatus capable of rapid operation.
Photoelectric solid-state relays using light-emitting diodes are known in the art. For example, U.S. Pat. No. 3,693,060 discloses a solid-state relay using an LED to energize a photosensitive FET connected to the gate electrodes of a pair of SCR's. And U.S. Pat. No. 3,418,480 discloses a lighting control circuit employing photocells and gas diodes to operate semiconductor switches.
Aiken U.S. Pat. No. 3,395,333 discloses a low-level circuit in which an incandescent lamp is biased to just below the point of incandescence where the resistance of the photocell is about to change or has changed to an insignificant degree to warm up the bulb so that shorting out the series resistor with a switch causes the photocell resistance to change rapidly. A search in class 250, subclasses 551, 552 and class 317, subclass 124 uncovered the following additional representative prior art:
______________________________________ 3,704,376 - Lehovec 3,040,178 - Lyman 3,461,316 - Acton 2,838,719 - Chitty 3,342,996 - Crusinberry 3,136,926 - Smith 3,240,943 - White 3,486,029 - Barrett et al. 3,202,905 - Gomez 3,708,672 - Marinkovic 3,185,850 - Terlet ______________________________________
Most of these other patents fall into three basic categories of photoelectric couplers:
1. Simple two element couplers, employing different types of emitters or sensors, with usefulness for signal data transfer.
2. Simple couplers augmented by additional circuits to enhance the transfer of signal data in terms of speed or efficiency.
3. Simple couplers augmented by additional circuits to perform low power relay functions.
It is an important object of this invention to provide solid-state relays having one or more of the following features:
1. Capability of operation from very low power circuits such as MOS (Metal Oxide Semiconductor) integrated circuits.
2. High speed operation without requiring semiconductor light sensors.
3. Input and output transient immunity.
4. Good thermal characteristics.
5. Commutating voltage derivative effects at high temperatures and low power factors.
6. Reliable operation over a wide range of temperatures.
7. Reliable operation in the presence of half-life degradation of LED's under continued use.
8. Convenient packaging.
9. Controlled turn-on time to reduce noise spike generation with inductive loads.
10. Relatively few parts.
11. High reliability.
12. Immunity to sensitivity degradation in a radioactive environment.
13. Circuit arrangement whereby excessive dissipation is likely to result in an OFF condition instead of an ON condition of the output solid-state device.